Partial properties: merging declarations and emit of simple cases (#7…

…2999)

src/Compilers/CSharp/Portable/Binder/BinderFactory.BinderFactoryVisitor.cs

@@ -288,6 +288,8 @@ public override Binder VisitAccessorDeclaration(AccessorDeclarationSyntax parent
                                     if ((object)propertySymbol != null)
                                     {
                                         accessor = (parent.Kind() == SyntaxKind.GetAccessorDeclaration) ? propertySymbol.GetMethod : propertySymbol.SetMethod;
+                                        // PROTOTYPE(partial-properties): check if a property with no accessors could fail this assertion, in which case we should either adjust the assertion or remove it.
+                                        Debug.Assert(accessor is not null || parent.HasErrors);
                                     }
                                     break;
                                 }
@@ -585,18 +587,25 @@ bool checkSymbol(Symbol sym, TextSpan memberSpan, SymbolKind kind, out Symbol re
                         return false;
                     }
 
-                    if (sym.Kind == SymbolKind.Method)
+                    if (kind is SymbolKind.Method or SymbolKind.Property)
                     {
                         if (InSpan(sym.GetFirstLocation(), this.syntaxTree, memberSpan))
                         {
                             return true;
                         }
 
-                        // If this is a partial method, the method represents the defining part,
-                        // not the implementation (method.Locations includes both parts). If the
-                        // span is in fact in the implementation, return that method instead.
-                        var implementation = ((MethodSymbol)sym).PartialImplementationPart;
-                        if ((object)implementation != null)
+                        // If this is a partial member, the member represents the defining part,
+                        // not the implementation (member.Locations includes both parts). If the
+                        // span is in fact in the implementation, return that member instead.
+                        if (sym switch
+#pragma warning disable format
+                            {
+                                MethodSymbol method => (Symbol)method.PartialImplementationPart,
+                                SourcePropertySymbol property => property.PartialImplementationPart,
+                                _ => throw ExceptionUtilities.UnexpectedValue(sym)
+                            }
+#pragma warning restore format
+                            is { } implementation)
                         {
                             if (InSpan(implementation.GetFirstLocation(), this.syntaxTree, memberSpan))
                             {

src/Compilers/CSharp/Portable/CSharpResources.resx

@@ -1171,7 +1171,7 @@
     <value>Cannot implicitly convert type '{0}' to '{1}'. An explicit conversion exists (are you missing a cast?)</value>
   </data>
   <data name="ERR_PartialMisplaced" xml:space="preserve">
-    <value>The 'partial' modifier can only appear immediately before 'class', 'record', 'struct', 'interface', or a method return type.</value>
+    <value>The 'partial' modifier can only appear immediately before 'class', 'record', 'struct', 'interface', or a method or property return type.</value>
   </data>
   <data name="ERR_ImportedCircularBase" xml:space="preserve">
     <value>Imported type '{0}' is invalid. It contains a circular base type dependency.</value>
@@ -7929,4 +7929,22 @@ To remove the warning, you can use /reference instead (set the Embed Interop Typ
   <data name="ERR_InterceptsLocationDataInvalidPosition" xml:space="preserve">
     <value>The data argument to InterceptsLocationAttribute refers to an invalid position in file '{0}'.</value>
   </data>
+  <data name="ERR_PartialPropertyMissingImplementation" xml:space="preserve">
+    <value>Partial property '{0}' must have an implementation part.</value>
+  </data>
+  <data name="ERR_PartialPropertyMissingDefinition" xml:space="preserve">
+    <value>Partial property '{0}' must have an definition part.</value>
+  </data>
+  <data name="ERR_PartialPropertyDuplicateDefinition" xml:space="preserve">
+    <value>A partial property may not have multiple defining declarations, and cannot be an auto-property.</value>
+  </data>
+  <data name="ERR_PartialPropertyDuplicateImplementation" xml:space="preserve">
+    <value>A partial property may not have multiple implementing declarations</value>
+  </data>
+  <data name="ERR_PartialPropertyMissingAccessor" xml:space="preserve">
+    <value>Property accessor '{0}' must be implemented because it is declared on the definition part</value>
+  </data>
+  <data name="ERR_PartialPropertyUnexpectedAccessor" xml:space="preserve">
+    <value>Property accessor '{0}' does not implement any accessor declared on the definition part</value>
+  </data>
 </root>

src/Compilers/CSharp/Portable/Errors/ErrorCode.cs

@@ -2310,6 +2310,14 @@ internal enum ErrorCode
         ERR_InterceptsLocationDataInvalidPosition = 9235,
         INF_TooManyBoundLambdas = 9236,
 
+        // PROTOTYPE(partial-properties): pack
+        ERR_PartialPropertyMissingImplementation = 9300,
+        ERR_PartialPropertyMissingDefinition = 9301,
+        ERR_PartialPropertyDuplicateDefinition = 9302,
+        ERR_PartialPropertyDuplicateImplementation = 9303,
+        ERR_PartialPropertyMissingAccessor = 9304,
+        ERR_PartialPropertyUnexpectedAccessor = 9305,
+
         #endregion
 
         // Note: you will need to do the following after adding errors:

src/Compilers/CSharp/Portable/Errors/ErrorFacts.cs

@@ -2438,6 +2438,13 @@ internal static bool IsBuildOnlyDiagnostic(ErrorCode code)
                 case ErrorCode.ERR_InterceptsLocationFileNotFound:
                 case ErrorCode.ERR_InterceptsLocationDataInvalidPosition:
                 case ErrorCode.INF_TooManyBoundLambdas:
+
+                case ErrorCode.ERR_PartialPropertyMissingImplementation:
+                case ErrorCode.ERR_PartialPropertyMissingDefinition:
+                case ErrorCode.ERR_PartialPropertyDuplicateDefinition:
+                case ErrorCode.ERR_PartialPropertyDuplicateImplementation:
+                case ErrorCode.ERR_PartialPropertyMissingAccessor:
+                case ErrorCode.ERR_PartialPropertyUnexpectedAccessor:
                     return false;
                 default:
                     // NOTE: All error codes must be explicitly handled in this switch statement

src/Compilers/CSharp/Portable/Symbols/MemberSymbolExtensions.cs

@@ -474,7 +474,7 @@ internal static bool ShouldEmit(this MethodSymbol method)
             }
 
             // Don't emit partial methods without an implementation part.
-            if (method.IsPartialMethod() && method.PartialImplementationPart is null)
+            if (method.IsPartialMember() && method.PartialImplementationPart is null)
             {
                 return false;
             }
@@ -545,22 +545,28 @@ internal static bool IsExplicitInterfaceImplementation(this Symbol member)
             }
         }
 
-        internal static bool IsPartialMethod(this Symbol member)
+        internal static bool IsPartialMember(this Symbol member)
         {
-            var sms = member as SourceMemberMethodSymbol;
-            return sms?.IsPartial == true;
+            return member
+                is SourceOrdinaryMethodSymbol { IsPartial: true }
+                or SourcePropertySymbol { IsPartial: true }
+                or SourcePropertyAccessorSymbol { IsPartial: true };
         }
 
         internal static bool IsPartialImplementation(this Symbol member)
         {
-            var sms = member as SourceOrdinaryMethodSymbol;
-            return sms?.IsPartialImplementation == true;
+            return member
+                is SourceOrdinaryMethodSymbol { IsPartialImplementation: true }
+                or SourcePropertySymbol { IsPartialImplementation: true }
+                or SourcePropertyAccessorSymbol { IsPartialImplementation: true };
         }
 
         internal static bool IsPartialDefinition(this Symbol member)
         {
-            var sms = member as SourceOrdinaryMethodSymbol;
-            return sms?.IsPartialDefinition == true;
+            return member
+                is SourceOrdinaryMethodSymbol { IsPartialDefinition: true }
+                or SourcePropertySymbol { IsPartialDefinition: true }
+                or SourcePropertyAccessorSymbol { IsPartialDefinition: true };
         }
 
         internal static bool ContainsTupleNames(this Symbol member)